Structure and hydrology of the Ogiri field, West Kirishima geothermal area, Kyushu, Japan

The geothermal system in the West Kirishima area is controlled by a system of faults and fractures oriented along two main directions, northwest to southeast and east±northeast to west±southwest. The Ginyu fault extends through the Ogiri ®eld in the Ginyu area, which is one of the east±northeast to west±southwest striking faults in this area. This fault is the reservoir target for developing the geothermal resources in the Ogiri ®eld. The Ginyu fault is a near planar fracture with a uniform temperature of 2328C and has near-neutral pH, chloride ¯uids. Based on the results of a detailed analysis of the Ginyu fault, all production wells drilled in the Ogiri ®eld intersected the Ginyu fault reservoir successfully, securing steam production for a 30 MWe power plant. A typical fracture-type geothermal model for the Ogiri ®eld was developed on the basis of the geology, electric and geophysical logs, ¯uid chemistry, and well test data. 7 2000 CNR. Published by Elsevier Science Ltd. All rights reserved.